[PATCH 1/2] Btrfs: fix kernel oops while reading compressed data

Liu Bo
2017-09-21T00:52:10Z

The kernel oops happens at

kernel BUG at fs/btrfs/extent_io.c:2104!
...
RIP: clean_io_failure+0x263/0x2a0 [btrfs]

It's showing that read-repair code is using an improper mirror index.
This is due to the fact that compression read's endio hasn't recorded
the failed mirror index in %cb->orig_bio.

With this, btrfs's read-repair can work properly on reading compressed
data.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reported-by: Paul Jones <paul@pauljones.id.au>
---
fs/btrfs/compression.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index d2ef9ac..9a4ccdf 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -107,6 +107,7 @@ static void end_compressed_bio_read(struct bio *bio)
struct inode *inode;
struct page *page;
unsigned long index;
+ unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
int ret;

if (bio->bi_status)
@@ -118,6 +119,14 @@ static void end_compressed_bio_read(struct bio *bio)
if (!refcount_dec_and_test(&cb->pending_bios))
goto out;

+ /*
+ * Record the correct mirror_num in cb->orig_bio so that
+ * read-repair can work properly.
+ */
+ ASSERT(btrfs_io_bio(cb->orig_bio));
+ btrfs_io_bio(cb->orig_bio)->mirror_num = mirror;
+ cb->mirror_num = mirror;
+
inode = cb->inode;
ret = check_compressed_csum(BTRFS_I(inode), cb,
(u64)bio->bi_iter.bi_sector << 9);
--
2.9.4